American Idol runner-ups are : Season 1- Justin Guarini . Season 2- Clay Aiken . Season 3- Diana Degarmo . Season 4- Bo Bice . Season 5- Katherine Mcphee . Season 6- Blake Lewis . Season 7- David Archuleta . Season 8- Adam Lambert . Season 9- Crystal Bowersox . I think that Adam Lambert is the most successful runner-up until now. David Archuleta is also successful.